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Benthic Marine Algae of Rotuma Island 409
119; Jaasund 1976: 71, fig. 142; Woelkerling 1976: 128, figs 219-222; Tsuda and Wray
1977: 106; Magruder and Hunt 1979: 69; Cribb 1983: 29, pl. 6, fig. 1; Lewis 1984: 11;
Tseng et al. 1984: 69, pl. 35, fig. 4; Payri and Meinesz 1985a: 512; Santelices and Stewart
1985: 21, fig. 6; Trono 1986: 262, fig. 71; Lewis and Norris 1987: 17; Silva et al. 1987: 25;
Garrigue and Tsuda 1988: 65; Littler et al. 1989: 172; Tsuda 1991: 52; Coppejans and
Prud'homme van Reine 1992a: 182; Norris 1992: 35, fig. 20; Ohba and Enomoto 1992: 31;
Price and Scott 1992: 25, fig. 4A-E; South and Yen 1992: 128; Millar and Kraft 1993: 11;
Verheij and Prud'homme van Reine 1993: 182; Wynne 1993: 9.
Fucus acerosus ForsskHl 1775: 190 (type locality: Mokha, Yemen).
Fucus rigidus Vahl 1802: 46 (type locality: St. Croix, Virgin Island).
Fucus spinifornzis Lamouroux 1805: 77, pl. XXXVI figs 3, 4 ('spinaeformis') (syntype
localities: Malagasy Republic; Mauritius).
Gelidium spiniforme (Lamouroux) Lamouroux 1813: 129; Montagne 1844: 662.
Sphaerococcus rigidus C. Agardh 1822a: 285.
Gelidium rigidum (C. Agardh) Greville 1830: vii; Dickie 1876: 243, 244; Okamura 1909
(1909-1912): 33, pl. 59, figs 1-6; Howe 1932: 169.
Gelidiopsis rigida (C. Agardh) Weber-van Bosse 1904a: 104; Okamura 1912 (1909-
1912): 188 (both 'rigidum').
Gelidiopsis rigida (Vahl) Weber-van Bosse 1928: 427, fig. 172 (sensu Womersley and
Bailey 1970).
Echinocaulon acerosum (ForsskHl) Borgesen 1932: 5, pl. 1, fig. 3 (sensu Womersley and
Bailey 1970).
(Figs 110, 120a, b)
Thallus up to 5 cm high, greenish-yellow to dull purple, tough and wiry with decumbent
basal parts attached by haptera and bearing free elongate, erect or arcuate-recurved
secondary branchlets. Branchlets 458-500 p,m in diameter, terete to slightly compressed, up
to 45 mm long and 1 mm in diameter, bearing terete filiform and determinate branchlets 2-8
mm long mostly secundly (sometimes radially) or bilaterally disposed. Apical cell about 12
pm in diameter, single and distinctly separated. External cortical cells anticlinally elongated;
internal cortical cells somewhat rounded, grading into a medulla of elongate cells about
12-18 pm in diameter, sometimes up to 30 Fm. Tetrasporic branches irregularly disposed,
with 26-30 oblong-cruciate sporangia up to 33 X 65 p,m progressively developed from the
apex, and irregularly disposed below the cortical cells. Cystocarps not seen.
Distribution
Tropical Indian and Pacific Oceans.
Fijian Records
Chapman 1971: 169; Kasahara 1985: 52; South 1991: 8; South and Kasahara 1992: 57; in
Herb Bishop Museum, Hawaii (BISH 530729,623672,623708,623720).
Rotuman Distribution
Hapmafau (HAP401 USP 421); Lopta (L171 USP 348, *L43/ USP S4: 19).
Habitat and Remarks
At Lopta, found on the outer reef crest in very exposed conditions associated with
Laurencia venusta Yamada and Chondria sedifolia Harvey, which together form the
dominant cover. At Hapmafau, however, the same species (albeit about half as large) is
found within Valonia aegagropila mats covering exposed beach rock or the back reef in
relatively sheltered conditions. Hence, this plant seems to be present in two extremes of
exposure at two opposite sites on the island, and has correspondingly different habits.